Project Summary Signaling by the Hedgehog (Hh) pathway plays a key role in the patterning and growth of many tissues in the embryo and defects in Hh signaling have profound pathological effects during embryonic development and during postnatal life. While we now have a very good understanding of both the mechanism by which Hh signals are transduced and the way in which Hh signaling controls cell fate and proliferation, there are many facets of this process that are unknown or have yet to be investigated. One example is the possibility that as cells respond to Hh signals differently depending on their cell cycle phase, a phenomenon we refer to as cell cycle gating. As cells progress through the cell cycle, they experience major changes with respect to cell volume, protein content, DNA content and organization of the cytoskeleton. Thus, it is reasonable to speculate that such large changes in cellular context would impact a cell's ability to respond to signaling proteins. Indeed, our preliminary data suggest that specific phases/subphases of the cell cycle are more or less permissive in terms of their transcriptional responses to Hh signals. The experiments proposed in Aim 1 will determine whether cell cycle gating of Hh transcriptional responses occurs at the level of the Hh signal transduction machinery and they will indicate the step in the pathway where cell cycle-gated inputs have their effects. In other experiments (Aim 2), we will determine how cell cycle progression affects transcriptional responses of all Hh targets. At the end of the project, we will have a much greater understanding of the importance of the cell cycle in controlling this pathway at both the mechanistic and transcriptome levels.